1. Field of the Invention
The present invention is directed to a PIN diode switch suitable for switching radio-frequency voltages.
2. Description of the Prior Art
A PIN diode switch of the type capable of switching radio-frequency voltages is described in "PIN-Diode Switches Excel In Wide-Bandwidth Use," Hartke, E.D.N. (Electrical Design News), Vol. 27, No. 18, Sept. 1982, pages 161-166. One of the PIN diodes switches disclosed therein consists of a series circuit of oppositely polarized PIN diodes disposed between the input and the output of the switch, with a control current supplied through another PIN diode to the junction of the series-connected PIN diodes. The drive circuit described in this article is suitable only for low radio-frequency voltages. In order to use the circuit to switch higher radio-frequency voltages, a higher reverse bias for the diodes would be required.
The general use of PIN diodes for RF-switches is known, for example, from the text "Signalverarbeitende Dioden," Kesel et al, 1982, pages 54-56. The generalized circuit diagrams described therein are reproduced as FIGS. 1 and 2 herein, and will be used to explain the general operation of such switches, as well as problems associated with conventional switches of this type.
As shown in FIG. 1, a PIN diode 1 is disposed between an input A and an output B of a switch. A control current I.sub.v1, or a control voltage U.sub.v1, is applied to the PIN diode 1. The PIN diode 1 is in a conductive condition as long as it is not charged with a control voltage U.sub.v1 in the non-conducting direction, as a reverse bias.
As shown in FIG. 2, PIN diodes can also be used in a switchover circuit, by using a further PIN diode 1' connecting the input A to a second output C. The PIN diodes 1 and 1', for example, can be alternatingly charged with blocking voltages.
In this known circuit design, the radio-frequency voltage to be switched is limited in amplitude by the available reverse bias U.sub.v1. The reverse bias U.sub.v1 cannot be permitted to be higher than the maximum permissible blocking voltage of the PIN diodes 1 or 1'. A high-voltage power pack is thus required for generating such high reverse biases, which is relatively complex to design.